This research plan exploits a series of cloned cell lines which differs in the kinetics of tumor development, the site of primary organ disease, the expression of several surface antigens, and glucocorticoid responsiveness. All the cell lines originated from a single AKR spontaneous T lymphoma and were derived using three approaches: (1)\the original cell line was cloned; (2)\in vitro selection methods were applied which were designed to isolate subclones with differing phenotypes, and (3)\cell clones were obtained from various tissues of animals following in vivo inoculation. A number of phenotypic alterations characteristic of T-cell maturation stages have been identified among these cell clones. The purpose of this work is to examine the extent and molecular nature of the phenotypic heterogeneity and to relate those differences to tumorigenicity and tumor progression in syngeneic animals. The goal of our research plan is to isolate the genes which are differentially expressed between T-lymphoma cell clones which differ significantly in tumorigenicity and in vivo growth properties. The phenotypic differences in the expression of surface antigens already identified will provide assays with which to monitor the effectiveness of the proposed methods to isolate differentially expressed genes. The regulation of the differentially expressed genes will be examined by measuring the transcription rates and DNA methylation patterns. Concurrent experiments will be undertaken to test whether the poorly tumorigenic cell clone can give rise to a more tumorigenic phenotype upon serial passage in vivo. Differential gene expression will be compared between the in vivo-derived tumorigenic cell line and an original highly tumorigenic clone. The research combining molecular, cellular, and animal studies will yield new and valuable information on tumor cell heterogeneity and tumor progression. (S)